Circuit substrate having a circuit pattern and method for making the same

ABSTRACT

A circuit substrate includes: an insulative substrate formed with a pattern of a recess, the recess being defined by a recess-defining wall that has a bottom wall surface and a surrounding wall surface extending upwardly from the bottom wall surface; a patterned metallic layer structure including at least a patterned active metal layer disposed within the recess, formed on the bottom wall surface of the recess-defining wall, and spaced apart from the surrounding wall surface of the recess-defining wall, the patterned active metal layer containing an active metal capable of initiating electroless plating; and a primary metal layer plated on the patterned metallic layer structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) of U.S. patent application Ser. No. 13/035,531, filed on Feb. 25, 2011, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a circuit substrate having a circuit pattern and a method for making the same, and more particularly to a circuit substrate having a circuit pattern formed in a recess in a substrate.

2. Description of the Related Art

Conventionally, methods of forming a circuit substrate having a circuit pattern on an insulative substrate can be performed by insert molding the circuit pattern into the insulative substrate or by laminating the circuit pattern with the insulative substrate. However, the aforesaid conventional methods can undesirably increase the thickness of the circuit substrate. Moreover, when the circuit pattern is modified or changed, adjustment of manufacturing equipments in the processing steps of the conventional method is time consuming.

U.S. Pat. No. 4,865,873 discloses a method for making a circuit substrate having a circuit pattern on a substrate. The method includes forming an insulating layer on a substrate, forming a water-soluble layer on the insulating layer, forming a patterned hole extending through the water-soluble layer and the insulating layer by laser ablation, forming an active metal layer in the patterned hole and on the water-soluble layer, and simultaneously electroless depositing a primary metal layer on the active metal layer and dissolving the water-soluble layer in an aqueous plating solution. Since the active metal layer covers a hole wall of the patterned hole as well as the water-soluble layer, electroless plating of the primary metal layer takes place not only at the hole wall but also at the surface of the water-soluble layer, which is undesirable. Although the water-soluble layer will be gradually dissolved in the aqueous plating solution during electroless plating, it can have an adverse effect on electroless plating. In addition, the thickness of the circuit substrate thus formed is considerably increased.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a circuit substrate that can overcome the aforesaid drawbacks associated with the prior art.

According to one aspect of the present invention, there is provided a circuit substrate that comprises: an insulative substrate having a top surface and formed with a pattern of a recess that is indented from the top surface, the recess being defined by a recess-defining wall that has a bottom wall surface and a surrounding wall surface extending upwardly from the bottom wall surface; a patterned metallic layer structure including at least a patterned active metal layer that is disposed within the recess, that is formed on the bottom wall surface of the recess-defining wall, and that is spaced apart from the surrounding wall surface of the recess-defining wall, the patterned active metal layer containing an active metal capable of initiating electroless plating, a pattern of the patterned active metal layer corresponding in shape to the pattern of the recess; and a primary metal layer plated on the patterned metallic layer structure.

According to another aspect of the present invention, there is provided a method for making a circuit substrate having a circuit pattern. The method comprises: (a) providing an insulative substrate having a top surface; (b) forming a pattern of a recess in the insulative substrate such that the recess is indented from the top surface, the recess being defined by a recess-defining wall having a bottom wall surface and a surrounding wall surface extending upwardly from the bottomwall surface; (c) forming a metallic layer structure on the recess-defining wall of the recess and the top surface of the insulative substrate, the metallic layer structure including at least one active metal layer containing an active metal capable of initiating electroless plating; (d) removing a portion of the metallic layer structure that is disposed along a peripheral edge of the bottom wall surface of the recess-defining wall so as to form the metallic layer structure into a first region which is disposed on the bottom wall surface, and a second region which is physically separated from the first region; and (e) plating a primary metal layer on the first region of the metallic layer structure.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

FIG. 1 is a perspective view illustrating a first step of a method for making the first preferred embodiment of a circuit substrate according to the present invention;

FIG. 2 is a perspective view illustrating a second step of the method for making the first preferred embodiment;

FIG. 3 is a schematic view taken along line III-III of FIG. 2;

FIG. 4 is a perspective view illustrating a third step of the method for making the first preferred embodiment;

FIG. 5 is a schematic view taken along line V-V of FIG. 4;

FIG. 6 is a schematic view illustrating a fourth step of the method for making the first preferred embodiment;

FIG. 7 is a schematic view illustrating a fifth step of the method for making the first preferred embodiment;

FIG. 8 is a perspective view illustrating a sixth step of the method for making the first preferred embodiment;

FIG. 9 is a schematic view taken along line IX-IX of FIG. 8;

FIG. 10 is a schematic view illustrating a first step of a method for making the second preferred embodiment of a circuit substrate according to the present invention;

FIG. 11 is a schematic view illustrating a second step of the method for making the second preferred embodiment;

FIG. 12 is a schematic view illustrating a third step of the method for making the second preferred embodiment;

FIG. 13 is a schematic view illustrating a fourth step of the method for making the second preferred embodiment;

FIG. 14 is a schematic view illustrating a fifth step of the method for making the second preferred embodiment;

FIG. 15 is a schematic view illustrating a first step of a method for making the third preferred embodiment of a circuit substrate according to the present invention;

FIG. 16 is a schematic view illustrating a second step of the method for making the third preferred embodiment;

FIG. 17 is a schematic view illustrating a third step of the method for making the third preferred embodiment;

FIG. 18 is a schematic view illustrating a fourth step of the method for making the third preferred embodiment; and

FIG. 19 is a schematic view illustrating a fifth step of the method for making the third preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the present invention is described in greater detail with reference to the accompanying preferred embodiments, it should be noted herein that like elements are denoted by the same reference numerals throughout the disclosure.

FIGS. 8 and 9 illustrate the first preferred embodiment of a circuit substrate 100 according to the present invention. The circuit substrate 100 includes: an insulative substrate 2 having a top surface 21 and formed with a pattern of a recess 20 that is indented from the top surface 21, the recess 20 being defined by a recess-defining wall 20′ that has a bottom wall surface 201 and a surrounding wall surface 202 extending upwardly from the bottom wall surface 201; a patterned metallic layer structure 5 including at least one patterned active metal layer 3 disposed within the recess 20, formed on the bottom wall surface 201 of the recess-defining wall 20′, and spaced apart from the surrounding wall surface 202 of the recess-defining wall 20′ by a gap 203, a patterned active metal layer 3 containing an active metal capable of initiating electroless plating, the pattern of the patterned active metal layer 3 corresponding in shape to the pattern of the recess 20; and a primary metal layer 4 electroplated on the patterned metallic layer structure 5. The patterned metallic layer structure 5 and the primary metal layer 4 cooperatively form a circuit pattern 10 that corresponds in shape to the pattern of the recess 20. Preferably, the circuit pattern 10 has a top surface 101 substantially flush with or disposed slightly above the top surface 21 of the substrate 2.

FIGS. 1 to 9 illustrate consecutive steps of a method for making the circuit substrate 100 of the first preferred embodiment according to the present invention. The method includes the steps of: (a) providing an insulative substrate 2 having a top surface 21 (see FIG. 1); (b) forming a pattern of a recess 20 in the insulative substrate 2 such that the recess 20 is indented from the top surface 21 (see FIGS. 2 and 3); (c) forming a metallic layer structure 5′ on a recess-defining wall 20′ of the recess 20 and the top surface 21 of the insulative substrate 2, the metallic layer structure 5′ including at least one active metal layer 3′ containing an active metal capable of initiating electroless plating (see FIGS. 4 and 5); (d) removing a closed-loop portion of the metallic layer structure 5′ that is disposed along a peripheral edge of a bottom wall surface 201 of the recess-defining wall 20′ so as to form the metallic layer structure 5′ into a first region 51 which is disposed on the bottom wall surface 201, and a second region 52 which is physically separated from the first region 51 by a gap 203 (see FIG. 6), the first region 51 of the metallic layer structure 5′ defining the patterned metallic layer structure 5 of FIG. 9, the active metal layer 3′ of the first region 51 of the metallic layer structure 5′ defining the patterned active metal layer 3 of FIG. 9; (e) electroplating a primary metal layer 4 on the first region 51 of the metallic layer structure 5′ (see FIG. 7); and (f) removing the second region 52 of the metallic layer structure 5′ from the insulative substrate 2 by electrolysis (see FIGS. 8 and 9).

In this embodiment, the active metal of the active metal layer 3′ is a reduced active metal. The metallic layer structure 5′ is formed on the recess-defining wall 20′ of the recess 20 and the top surface 21 of the insulative substrate 2 in step (c) by immersing the insulative substrate 2 into an active metal solution containing a non-reduced active metal (not shown) so as to form a non-reduced metal layer containing the non-reduced active metal on the recess-defining wall 20′ of the recess 20 and the top surface 21 of the insulative substrate 2 and then reducing the non-reduced active metal of the non-reduced metal layer so as to form the active metal layer 3′ containing the reduced active metal on the recess-de fining wall 20′ of the recess 20 and the top surface 21 of the insulative substrate 2. The primary metal layer 4 is plated on the first region 51 of the metallic layer structure 5′ by electroplating techniques.

In this invention, the non-reduced active metal of the non-reduced metal layer is in the form of active metal colloid particles or metal ions.

Preferably, the active metal is selected from the group consisting of palladium, rhodium, platinum, iridium, osmium, gold, nickel, iron, and combinations thereof.

Preferably, the active metal solution containing the non-reduced active metal is palladium salt solution or palladium-tin colloid solution.

Preferably, the primary metal layer 4 is made from a metal selected from the group consisting of copper, nickel, silver, and gold.

Preferably, the insulative substrate 2 is made from a material selected from the group consisting of polycarbonate, a combination of acryl resin and acrylonitrile butadiene styrene (ABS) resin, and a combination of polycarbonate and ABS resin.

Preferably, the recess 20 in the insulative substrate 2 is formed by laser or plasma ablation.

Preferably, the closed-loop portion of the metallic layer structure 5′ is removed by laser ablation.

FIG. 14 illustrates the second preferred embodiment of a circuit substrate 100 according to the present invention. The second preferred embodiment differs from the previous embodiment in that the active metal of the patterned active metal layer 3 is a non-reduced active metal, that the patterned metallic layer structure 5 further includes an intermediate metal layer 6 which is electroless plated on the patterned active metal layer 3 and which has a pattern corresponding to that of the active metal layer 3, and that the primary metal layer 4 is electroplated on the intermediate metal layer 6. The patterned metallic layer structure 5 and the primary metal layer 4 cooperatively form the circuit pattern 10.

FIGS. 10 to 14 illustrate consecutive steps of a method for making the circuit substrate 100 of the second preferred embodiment according to the present invention. The method includes the steps of: forming a pattern of a recess 20 in the insulative substrate 2 (see FIG. 10); forming a metallic layer structure 5′ on a recess-defining wall 20′ of the recess 20 and a top surface 21 of the insulative substrate 2 by immersing the insulative substrate 2 into an active metal solution containing a non-reduced active metal (not shown) so as to form an active metal layer 3′ containing the non-reduced active metal on the recess-defining wall 20′ of the recess 20 and the top surface 21 of the insulative substrate 2 (see FIG. 10) and then electroless plating an intermediate metal layer 6 on the active metal layer 3′ (see FIG. 11); removing a portion of the metallic layer structure 5′ that is disposed along a peripheral edge of a bottom wall surface 201 of the recess-defining wall 20′ so as to form the metallic layer structure 5′ into a first region 51′ which is disposed on the bottom wall surface 201, and a second region 52′ which is physically separated from the first region 51′ by a gap 203 (see FIG. 12), the first region 51′ of the metallic layer structure 5′ defining the patterned metallic layer structure 5 of FIG. 14, the active metal layer 3′ of the first region 51′ of the metallic layer structure 5′ defining the patterned active metal layer 3 of FIG. 14; (e) electroplating a primary metal layer 4 on the intermediate metal layer 6 of the first region 51′ of the metallic layer structure 5′ (see FIG. 13); and (f) removing the second region 52′ of the metallic layer structure 5′ from the insulative substrate 2 by electrolysis (see FIG. 14).

FIG. 19 illustrates the third preferred embodiment of a circuit substrate 100 according to the present invention. The third preferred embodiment differs from the first preferred embodiment in that the active metal of the patterned active metal layer 3 is a non-reduced active metal, that the primary metal layer 4 is electroless plated on the patterned active metal layer 3, and that a top metal layer 7 is formed on the primary metal layer 4. Although the way of making the third preferred embodiment is different from that of the second preferred embodiment, the third preferred embodiment has a structure similar to that of the second preferred embodiment as the primary metal layer 4 and the top metal layer 7 of the third preferred embodiment are equivalent to the intermediate metal layer 6 and the primary metal layer 4 of the second preferred embodiment, respectively.

FIGS. 15 to 19 illustrate consecutive steps of a method for making the circuit substrate 100 of the third preferred embodiment according to the present invention. The method includes the steps of: forming a pattern of a recess 20 in the insulative substrate 2 (see FIG. 15); forming a metallic layer structure 5′ on a recess-defining wall 20′ of the recess 20 and a top surface 21 of the insulative substrate 2 by immersing the insulative substrate 2 into an active metal solution containing a non-reduced active metal (not shown) so as to form an active metal layer 3′ containing the non-reduced active metal on the recess-defining wall 20′ of the recess 20 and the top surface 21 of the insulative substrate 2 (see FIG. 15); removing a portion of the metallic layer structure 5′ that is disposed along a peripheral edge of a bottom wall surface 201 of the recess-defining wall 20′ so as to form the metallic layer structure 5′ into a first region 51 which is disposed on the bottom wall surface 201, and a second region 52 which is physically separated from the first region 51 by a gap 203 (see FIG. 16), the first region 51 of the metallic layer structure 5′ defining the patterned metallic layer structure 5 of FIG. 19, the active metal layer 3′ of the first region 51 of the metallic layer structure 5′ defining the patterned active metal layer 3 of FIG. 19; (e) electroless plating a primary metal layer 4 on the active metal layer 3′ of the first region 51 of the metallic layer structure 5′ (see FIG. 17); electroplating a top metal layer 7 on the primary metal layer 4 (see FIG. 18); and (f) removing the second region 52 of the metallic layer structure 5′ from the insulative substrate 2 by electrolysis (see FIG. 19).

By forming a recess 20 in the insulative substrate 2 and a metallic layer structure 5′ including at least one active metal layer 3′ (which is formed by contacting the insulative substrate 2 with an active metal solution) in the recess 20 and subsequently removing a portion of the metallic layer structure 5′ from the insulative substrate 2 according to the method of this invention, the aforesaid drawbacks associated with the prior art can be alleviated.

While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements. 

1. A circuit substrate comprising: an insulative substrate having a top surface and formed with a pattern of a recess that is indented from said top surface, said recess being defined by a recess-defining wall that has a bottom wall surface and a surrounding wall surface extending upwardly from said bottom wall surface; a patterned metallic layer structure including at least a patterned active metal layer that is disposed within said recess, that is formed on said bottom wall surface of said recess-defining wall, and that is spaced apart from said surrounding wall surface of said recess-defining wall, said patterned active metal layer containing an active metal capable of initiating electroless plating, a pattern of said patterned active metal layer corresponding in shape to the pattern of said recess; and a primary metal layer plated on said patterned metallic layer structure.
 2. The circuit substrate of claim 1, wherein said active metal is selected from the group consisting of palladium, rhodium, platinum, iridium, osmium, gold, nickel, iron, and combinations thereof.
 3. The circuit substrate of claim 1, wherein said primary metal layer is made from a metal selected from the group consisting of copper, nickel, silver, and gold.
 4. The circuit substrate of claim 1, wherein said insulative substrate is made from a material selected from the group consisting of polycarbonate, a combination of acryl resin and acrylonitrile butadiene styrene (ABS) resin, and a combination of polycarbonate and ABS resin.
 5. The circuit substrate of claim 1, wherein said active metal is reduced.
 6. The circuit substrate of claim 1, wherein said active metal is non-reduced, said patterned metallic layer structure further including an intermediate metal layer electroless plated on said patterned active metal layer, said primary metal layer being electroplated on said intermediate metal layer.
 7. A method for making a circuit substrate having a circuit pattern, the method comprising: (a) providing an insulative substrate having a top surface; (b) forming a pattern of a recess in the insulative substrate such that the recess is indented from the top surface, the recess being defined by a recess-defining wall having a bottom wall surface and a surrounding wall surface extending upwardly from the bottom wall surface; (c) forming a metallic layer structure on the recess-defining wall of the recess and the top surface of the insulative substrate, the metallic layer structure including at least one active metal layer containing an active metal capable of initiating electroless plating; (d) removing a portion of the metallic layer structure that is disposed along a peripheral edge of the bottom wall surface of the recess-defining wall so as to form the metallic layer structure into a first region which is disposed on the bottom wall surface, and a second region which is physically separated from the first region; and (e) plating a primary metal layer on the first region of the metallic layer structure.
 8. The method of claim 7, wherein, in step (c), the active metal of the active metal layer is a reduced active metal, and the metallic layer structure is formed on the recess-defining wall of the recess and the top surface of the insulative substrate by immersing the insulative substrate into an active metal solution containing a non-reduced active metal so as to form a non-reduced metal layer containing the non-reduced active metal on the recess-defining wall of the recess and the top surface of the insulative substrate and then reducing the non-reduced active metal of the non-reduced metal layer so as to form the active metal layer containing the reduced active metal.
 9. The method of claim 8, wherein, in step (e), the primary metal layer is formed on the first region of the metallic layer structure by electroplating.
 10. The method of claim 7, wherein, in step (c), the active metal of the active metal layer is a non-reduced active metal, and the metallic layer structure is formed on the recess-defining wall of the recess and the top surface of the insulative substrate by immersing the insulative substrate into an active metal solution containing the non-reduced active metal so as to form the active metal layer containing the non-reduced active metal on the recess-defining wall of the recess and the top surface of the insulative substrate and then electroless plating an intermediate metal layer on the active metal layer.
 11. The method of claim 10, wherein, in step (e), the primary metal layer is formed on the intermediate metal layer of the first region of the metallic layer structure by electroplating.
 12. The method of claim 7, wherein, in step (c), the active metal of the active metal layer is a non-reduced active metal, and the metallic layer structure is formed on the recess-defining wall of the recess and the top surface of the insulative substrate by immersing the insulative substrate into an active metal solution containing the non-reduced active metal so as to form the active metal layer containing the non-reduced active metal on the recess-defining wall of the recess and the top surface of the insulative substrate.
 13. The method of claim 12, wherein, in step (e), the primary metal layer is formed on the active metal layer of the first region of the metallic layer structure by electroless plating.
 14. The method of claim 13, further comprising, after step (e), electroplating a top metal layer on the primary metal layer.
 15. The method of claim 7, wherein, in step (b), the recess in the insulative substrate is formed by laser or plasma ablation.
 16. The method of claim 7, wherein, in step (d), the portion of the metallic layer structure is removed by laser ablation.
 17. The method of claim 7, further comprising, after step (e), removing the second region of the metallic layer structure from the insulative substrate.
 18. The method of claim 17, wherein the second region of the metallic layer structure is removed from the insulative substrate by electrolysis. 